Pope Francis in his Christmas Eve mass on Sunday urged the world's 1.3 billion Catholics not to ignore the plight of migrants who are "driven from their land" because of leaders willing to shed "innocent blood".

"So many other footsteps are hidden in the footsteps of Joseph and Mary," the Argentine pontiff, himself the grandson of Italian migrants, told worshippers in Saint Peter's Basilica.

"We see the tracks of millions of persons who do not choose to go away but, driven from their land, leave behind their dear ones."

Many engulfed in the ongoing migration crisis were forced to flee from leaders "who, to impose their power and increase their wealth, see no problem in shedding innocent blood", said the 81-year-old, who will give his traditional Urbi et Orbi Christmas address on Monday.

The pontiff's plea for "hope" came as fresh tensions simmered in the West Bank following Washington's recognition of Jerusalem as Israel's capital.

Pope Francis strongly defended immigrants at his Christmas Eve Mass, comparing them to Mary and Joseph finding no place to stay in Bethlehem https://t.co/3SPNDTDPSF

The announcement by US President Donald Trump on 6 December triggered demonstrations and clashes, including in Bethlehem in the Israeli-occupied West Bank where Christians will mark the birth of Jesus at a midnight mass.

Palestinian scouts played drums and bagpipes at Christmas celebrations in Bethlehem on Sunday, but many tourists stayed away this year.

Hundreds of people gathered in the cold on Bethlehem's Manger Square to watch the annual scout parade towards the Church of the Nativity, built over the spot where tradition says Mary gave birth to Jesus.

But the square was noticeably quieter following the violence between Palestinian protesters and the Israeli army in the past weeks.

Twelve Palestinians have been killed since Trump's declaration, including a 19-year-old who died of his wounds on Sunday, nine days after he was shot during a Gaza protest.

In the square, Nahil Banura, a Christian woman from Beit Sahur, near Bethlehem, said Trump's decision had made the run-up to Christmas "miserable".

Trump's decision

"People are only going out to vent," she said.

Perhaps as few as 50,000 Palestinian Christians make up about two percent of the predominantly Muslim population of the West Bank and East Jerusalem.

Archbishop Pierbattista Pizzaballa, apostolic administrator of the Latin Patriarch of Jerusalem, visited the Church of the Nativity on Sunday afternoon.

He said last week that "dozens" of foreign visitors had cancelled their Christmas trips after Trump's announcement.

But Israel's tourism ministry said Christmas preparations have not been affected, and it expects a 20 percent increase in the number of Christian pilgrims this year compared with 2016.

An Israeli police spokesman said extra units will be deployed in Jerusalem and at the crossings to Bethlehem to ease the access for the "thousands of tourists and visitors".

Israel seized East Jerusalem in the 1967 Middle East war and later annexed it, in moves never recognised by the international community.

Palestinians view East Jerusalem as the capital of their future state, and interpreted Trump's statement as rejecting their right to a capital in east Jerusalem, although the Americans deny this.

Palestinian President Mahmoud Abbas said Trump's decision meant that any peace plan proposed by the US will be no longer acceptable.

Mitri Raheb, pastor of the Evangelical Lutheran Christmas Church in Bethlehem,​ told AFP on Sunday that Christmas this year is a "mix of sadness and joy" because of the US decision on Jerusalem, which he called "the beating heart of Palestine".